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Discharge.-- PLATTE RIVER BASIN 06701500 SOUTH PLATTE RIVER BELOW CHEESMAN RESERVOIR Location.-- Drainage and Period of Record.-- Lat. 39°12'33",Long. 105°16'02", in SE¼NW¼ sec.6, T.10 S., R.70 W., Jefferson County, Hydrologic Unit 10190002, on left bank 1,400 ft downstream from toe of Cheesman Dam and 3.8 mi southwest of Deckers. 1,752 mi². Oct.1, 1924-May 13, 1956 at site 370 feet upstream and 0.50 ft. higher. May 14, 1956 to present at current site. Unreliable record from 1909 to 1924 unpublished. Graphic water stage recorder and Sutron Satlink2 Data Collection Platform (DCP) with a Sutron 56-0540 shaft encoder (SE) in a wooden shelter over a concrete well adjacent to a 30-foot concrete Parshall flume. The chart recorder was replaced with a Sutron Stage Discharge Recorder (SDR) on September 10, 2009. No outside staff gage is present. The station and flume are owned and maintained by the Denver Water Board (DWB). The satellite equipment is owned and maintained by the Division of Water Resources (DWR). Equipment.-- Hydrographic Conditions.-- Gage-Height Record.-- Datum Corrections.-- Rating.-- Discharge.-- Special Computations.-- Remarks.-- Recommendations.-- Cheesman Reservoir is in the center of the 2002 Hayman burn area. The fire severely damaged the watershed and the Denver Water Board has performed extensive erosion control in the area surrounding the reservoir. Major revegetation efforts were performed in the burn area to reduce erosion and water quality problems. The primary record is hourly averages of 15-minute telemetered SE data with chart and SDR data as backup. The DCP suffered various failures of short duration or required maintenance throughout the year which caused the log to be incomplete. Data gaps occurred on: October 1 and 23, 2008; November 6, 7, 15, 16, 26, 2008; Dec 1, 2008; and August 4 -5, 2009. These gaps were filled in with chart data without loss of accuracy. Some interpretation of the exact time was occasionally required with the chart record (due to poorly adjusted clock), but this was accomplished with complete accuracy by bracketing change periods. Twenty-six visits were made to the gage and no SE adjustments were needed. Due to the flume’s proximity to the dam, ice accumulation in the approach, flume, and departing sections is not an issue. However, the flume is subject to moss and algal growth. Two flume cleaning corrections were made: -0.01 feet on October 20, 2008, prorated by time as a datum correction from the previous visit (date) when the flume was cleaned; and - 0.10 ft on February 24, 2009 addressed by incorporating the correction into shift for the measurement made that day. Levels were run on September 10, 2009 and the gage was found to be reading correctly. The control is a concrete 30-foot Parshall flume with a modified rating. The flume submerges at flows near the 1000 cfs due to constrictions in the channel below the gage. Rating No. 11 was developed in 1995 to compensate for submergence and was continued in use for the current year. Submergence seems to begin when the measurement section velocity reaches around 6.6 ft/s. The rating is well defined except for flows around 1,000 cfs where submergence appears to cause a break point in the slope of the curve. Shifts historically were within a few hundredths of the rating. However as the approach pool has filled, shifts have become more positive. Gravel deposition occurred on the left side of the upstream channel and the flume converging section during a precipitation event on 7/21/2009. The gravel was washed down the access road into the channel above the Parshall flume. Some effort was made to remove the material when the road was repaired; however a large delta remains causing higher velocities from the mid section to right edge of water in the flume. Comparisons of velocities to measurements taken in 1995 show the effects of the approach pool filling with elevated velocities at comparable depths. Using the USBR "Water Measurement Manual", a 30 ft Parshall Flume's range of accurately measuring discharge is 15 to 1500 cfs. Anything above or below this range is outside the +/- 5% accuracy. Given this fact, flows below 15 cfs at gage height 0.38, or above 1500 cfs at gage height of 5.94 the record would be considered fair. All flows in water year 2009 were within the +/- 5% range of accuracy. Twenty three measurements (Nos. 205-227) were made during the water year ranging in discharge from 37.9 to 878 cfs. The flume rating is well defined for the ranges of flow experienced. The peak discharge of 900 cfs occurred at 1630 June 3, 2009 at a gage height of 3.52 ft with a shift of +0.19 ft. It exceeded measurements Nos. 219, 220, made on June 4, 2009, by 0.06 feet in stage. Shifting control method was used all year. Negative shifts occur when moss accumulates on the crest of the flume. This was the case for the periods from 10/1/2008 to 2/24/2009 and from 9/2/2009 to 9/30/2009 when moss was noted to affect the stage discharge relationship. Shifts were applied as defined by measurements and distributed by time for this period. For the period from 2/24/2009 to 9/2/2009, variable shift table PLACHECOVST1 was applied with shifts distributed by stage. PLACHECOVST1 was developed from measurements # 212 through # 226 completed during the same period. Measurements 217 abd 223 were adjusted 1% and 2% to better fit the shift curve. Measurements for the entire water year show shifts varying from -0.05 ft. to 0.19 ft. Flume cleaning corrections are handled differently depending on whether the State or DWB perform the cleaning. If the gage height drops as a result of a DWB flume cleaning, it usually occurs between measurements, it is Denver’s procedure to increase the release so that the same gage height is maintained. This did not occur this year. If a gage height change occurs when the flume is cleaned by a State Hydrographer, a measurement is made before and after the flume cleaning with shifts applied accordingly. The record is considered good. Station maintained and record developed by Mike Wild . Remove gravel from weir pool. Install staff gage. 2009Water Year